Display device

ABSTRACT

The present invention relates to devices for displaying the previous history of products, e.g. in relation to the development of temperature. The device according to the invention comprises a surface layer, an indicator layer, an activator layer and an optional delaying layer. Heating releases moisture which migrates in some embodiments first into the delaying layer and then into the activator layer. Here, an activator is mobilized and migrates together with the humidity into the indicator layer. A colour change occurs as a result of the interaction of the indicator with the activator in the presence of moisture, which change indicates that the critical temperature has been exceeded. The present invention further relates to a method for producing the device according to the invention and to applications of said device, e.g. in monitoring the temperature of sensitive products.

RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national stage filing ofInternational Application No. PCT/EP2013/070328, filed Sep. 30, 2013,which claims priority to European Patent Application No. 12186803.8,filed Oct. 1, 2012. The entire contents of each of the foregoingapplications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to display devices and in particular todevices for recording and displaying the previous thermal history ofrefrigerated goods and in particular of deep frozen products. Moreover,it relates to methods for producing such devices and to the applicationof the devices according to the invention when monitoring the previousthermal history of refrigerated products and in particular deep frozenproducts.

PRIOR ART

Devices for displaying the previous thermal history of products (alsocalled “temperature/time indicators”) display whether the refrigerationchain of the product in question has been broken, i.e. whether theproduct has exceeded a critical temperature over a relevant period oftime. These types of display device are of particular interest for deepfrozen products. In this case the device indicates whether the producthas been able to heat up to a temperature above the critical temperatureof 0° C.

There is a great need for such display devices because if therefrigeration chain is broken, the desired product quality can no longerbe guaranteed. Thus, for example, with deep frozen foods there is a riskof uncontrolled bacteria growth if the deep freezing chain is broken.Such bacteria growth may conceal considerable health risks for theconsumer.

In consideration of this need a wide variety of attempts have been andare being made to develop suitable temperature/time indicators. One canname here, for example, the display device according to WO 2007/045424as well as the BASF OnVu ICE time/temperature indicators and indicatorsmade by the company Timestrip in 40549 Düsseldorf.

However, the time/temperature indicators known from the prior art arenot capable of reliably indicating interruptions in the refrigerationchain. On the one hand there is the risk that short-term heating of thepackaging (e.g. by the hands of the consumer in the supermarket) willlead to a false positive display. On the other hand, there is the riskwith the time/temperature indicators of the prior art that aninterruption to the refrigeration chain is not indicated as such ifthere is air between the refrigerated product and the display devicewithin the packaging.

Another problem which occurs, for example with the commercial indicatormade by the company Timestrip, is the uniformity of the colour changedisplayed (i.e. the consistent period of time between reaching acritical temperature of the indicator and the colourchange—independently of the nature of the refrigerated product). Suchuniformity is undesirable because many deep frozen products defrostconsiderably faster than others. A reliable display should take suchdifferences into consideration.

Summary of the invention

In consideration of the aforementioned problems associated with thetime/temperature indicators known from the prior art, the presentinvention is concerned with the object of providing a time/temperatureindicator which reliably displays breaks in the refrigeration chainwithout giving false positive displays and with which breaks in therefrigeration chain are reliably displayed, even if there is air betweenthe refrigerated product and the display device. Furthermore, thedisplay of the indicator according to the invention should take intoaccount the actual defrosting speed of the refrigerated product.

This object is achieved by the device which comprises the followinglayers:

-   -   (a) a surface layer (1) impermeable to moisture,    -   (b) an indicator layer (2) that comprises at least one        indicator,    -   (c) an activator layer (3) that comprises at least one        activator, and    -   (d) an optional delaying layer (4),    -   the surface layer being positioned over the indicator layer, the        activator layer and the delaying layer,    -   the indicator layer being positioned between the surface layer        and the optional delaying layer, and        the activator layer being able to be absent if an indicator that        is activated by H₂O is used.

Preferred configurations of this device are characterized below:

-   -   the device, wherein the indicator layer comprises a pH        indicator, preferably an anthocyanin colorant, and the activator        layer has an acid or an alkali as the activator;    -   the device, wherein the indicator layer and/or the activator        layer comprise a matrix material which is chosen from at least        one of agar-agar, carrageenan, gelatine, starch, gum arabic,        cellulose, arrowroot starch, guar gum and polyethylene glycol;    -   the device, wherein the indicator layer and/or the activator        layer contain at least one hygroscopic salt which is preferably        chosen from the group consisting of magnesium chloride,        potassium chloride and calcium chloride;    -   the device, wherein the delaying layer (d) is present and formed        from paper or cardboard with a thickness of 40-60 g/cm²        according to DIN 6730;    -   the device, wherein the activator layer (d) is formed from 2-30,        preferably 3-8, more preferably 4-6 sequential individual        layers;    -   the device, wherein the indicator layer (c) is formed from 2-40,        preferably 4-10, more preferably 6-8 sequential individual        layers;    -   the device, wherein the layers (a), (b), (c) and (d) are        arranged as follows:    -   (a) surface layer (1),    -   (b) indicator layer (2),    -   (c) optional delaying layer (4), and    -   (d) activator layer (3),        or    -   (a) surface layer (1),    -   (b) activator layer (3),    -   (c) indicator layer (2), and    -   (d) optional delaying layer (4),        or    -   (a) surface layer (1),    -   (b) indicator layer (2),    -   (c) activator layer (3), and    -   (d) optional delaying layer (4);    -   the device as described above which is applied to packaging of a        product;    -   the device as described above which is applied to packaging of a        product, wherein the product is refrigerated and wherein a        period of time between first defrosting of the product and color        change of the indicator is in the range of 0.5 hours to 3 hours.

The present invention further relates to methods for producing thedisplay devices according to the invention. These methods arecharacterized below.

-   -   A method, wherein one or more of the layers present in the        device are formed by carrying out procedural steps (i) and (ii)        sequentially one or more times:    -   (i) printing and    -   (ii) drying the printed layer.    -   A method selected from the following methods:        -   a method which comprises the following steps:            -   (A-1) providing the surface layer (1),            -   (A-2) coating the surface layer (1) with the indicator                layer (2),            -   (A-3) drying the indicator layer (2) to produce an                arrangement (A);            -   (B-1) providing a delaying layer (4),            -   (B-2) coating the delaying layer (4) with the activator                layer (3),            -   (B-3) drying of the activator layer (3) to produce an                arrangement (B);            -   (C) laminating the arrangements (A) and (B) and        -   a method which comprises the following steps:            -   (A′-1) providing the surface layer (1),            -   (A′-2) coating the surface layer (a) with the activator                layer (3),            -   (A′-3) drying the activator layer (3) to produce an                arrangement (A′)            -   (B′-1) providing a delaying layer (d)            -   (B′-2) coating the delaying layer (d) with the indicator                layer (2),            -   (B′-3) drying the indicator layer (2) to produce an                arrangement (B′)            -   (C′) laminating the arrangements (A′) and (B′).

A method, wherein a first layer, chosen from the surface layer and thedelaying layer, is provided; and wherein the other layers of the deviceare applied sequentially according to the sequence of their arrangementin the device; and wherein at least upon applying the indicator layerand the activator layer the layer which is applied first is dried priorto applying a subsequent layer, and the component or components of thesubsequent layer are provided and applied in a highly volatile organicsolvent if no additional layer is provided between the indicator layerand the activator layer.

Finally, the present invention also relates to packaging for deep frozenproduct comprising the device as described above, and to the deep frozenproducts comprising this packaging.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the layer sequence of the device according to theinvention in its simplest configuration.

FIG. 2 illustrates the layer sequence of the device according to theinvention in another configuration with adhesive layers.

FIGS. 3 to 13 illustrate the layer sequences of other devices accordingto the invention.

The reference numbers used in the figures signify as follows:

-   1—surface layer (a)-   2—indicator layer (b)-   3—activator layer (c)-   4—delaying layer (d)-   4′—delaying layer (d) as a component part of the product packaging-   5—upper adhesive layer-   6—middle adhesive layer-   7—lower adhesive layer-   8—separating layer

DETAILED DESCRIPTION OF THE INVENTION Definitions

In connection with the present invention the term “indicator” relates toa substance which, upon interacting (chemical or physical reaction) withthe activator, changes its visual appearance. This includes inparticular a colour change, the colours (including colourless) not beingdetermined before and after the colour change.

In connection with the present invention the term “activator” relates toa substance which, as a result of the interaction with the indicator, issuitable for bringing about a change to the visual appearance of theindicator.

The suitability of a substance as an indicator or an activator in thesense of the present invention depends upon the identity of therespective reactant. Therefore, fulfillment of the “indicator” criterionis always to be tested in connection with fulfillment of the “activator”criterion (and vice versa). The suitability of the indicator alsoincludes the presence of the indicator in a form suitable for reactionwith the activator, e.g. the presence of a pH indicator in protonatedform if the activator is an alkali or the presence of a pH indicator inthe deprotonated form if the activator is an acid.

In connection with the present invention the specification of the“period of time between the start of defrosting and the colour change”(also called “change time” in this application) relates to the period oftime which can be measured until a colour change can be seen with thenaked eye if a deep frozen pea product (300 g, deep frozen temperature−18° C., standard packaging, no film on the inside, only 320 g/m²cardboard outer packaging) is brought into a room temperatureenvironment (wooden table below, air to the side and above, respectivelybrought to a temperature of +20° C.).

The change time is essentially determined by the “overall delayingeffect” of the “relevant layers”. The “overall delaying effect” meansthe period of time that is required for an amount of moisture sufficientfor the colour change to migrate from the refrigerated product, throughall relevant layers, to the uppermost colouring layer. In thisconnection the term “relevant layers” refers to all of the layers of thedevice according to the invention from the lowermost layer to andincluding the uppermost colouring layer. The product packaging lyingbeneath the device according to the invention is also a relevant layerdetermining the overall delaying effect. If the type of productpackaging is not known, in order to determine the overall delayingeffect one is to assume the use of cardboard packaging with a thicknessof 320 g/m².

It is an essential feature of the device according to the invention thatit is dry prior to the penetration of moisture from the refrigeratedproduct. In this connection “dry” means a moisture content that is sosmall that the colour reaction, which leads to the desired colourchange, does not take place to an extent that can be seen with the nakedeye. This applies in particular to the anticipated storage conditions,i.e. for example to storage of the device according to the invention at25° C. and <5% relative air humidity over a period of 2 months,preferably 6 months. Preferably, a colour reaction that can be seen withthe naked eye does not take place either when the device according tothe invention is stored at −18° C. and 100% relative air humidity for 12months, preferably 24 months.

Unless specified to the contrary in the present application, the termsused here have the generally customary meaning in the technical field inquestion as can be taken e.g. from appropriate lexica, specialistdictionaries and encyclopaedias.

Grammages of paper and cardboard relate to grammages according to DIN6730. For films, specified grammages relate to DIN 53352. Specified filmthicknesses relate to DIN 53370.

Overview

Surprisingly, it has now been found that the moisture that is formed byheating deep frozen products to temperatures of above 0° C. within thepackaging migrates in sufficient quantities through the packaging of thedeep frozen products so as to be able to trigger chemical reactions onits outside. The present invention utilises this knowledge in order toindicate heating to above the freezing point: Upon heating to above thefreezing point, moisture is released by the partial defrosting of therefrigerated product. Part of this moisture migrates through thepackaging to the display device according to the invention. The moisturepenetrates into the device according to the invention. The indicatorand/or the activator are solubilised or mobilised by the moisture here.As a result, the previously spatially separated indicator and activatorcomponents are brought together. When these two components meet, achemical or physical reaction takes place which leads to a colourchange. This colour change serves to indicate the heating of the productto a temperature above the temperature at which the refrigerated productstarts to defrost.

The sensitivity of the device according to the invention can beincreased by using materials with particularly pronounced hygroscopy(e.g. as a matrix material of the indicator and/or activator layerdescribed in more detail below). However, limits are set for thismeasure by the required storage stability. Particularly hygroscopicmaterials will already “draw” a large amount of moisture when stored fora short time under average moisture conditions, and so trigger anundesired premature colour reaction.

The mode of operation of the device according to the invention is basedon the moisture released from the refrigerated product upon defrosting.Consequently, with the device according to the invention it is neithernecessary for nor is provision made such that there are moisturereservoirs in one or a number of the layers of the device according tothe invention.

The required duration of exceedance of the minimum defrostingtemperature of the refrigerated product until there is a colour changecan be set by an appropriate choice of layer materials used or of theirthicknesses.

The device according to the invention is characterised in that noadaptation of the underlying product packaging is required (if thelatter is made of cardboard or of some other moisture-permeablematerial). In particular, no opening in the product packaging and no“wick” through the product packaging either is required.

Another essential aspect of the present invention is the possibility ofproducing the device according to the invention layer by layer using anestablished printing process such as e.g. an offset or flexographicprinting process.

Layer Sequence

As explained above, the present invention is based on the spatialseparation of the indicator and the activator by providing thesecomponents in separate layers.

Other essential elements of the device according to the invention are asurface layer (1), which protects the device from moisture towards theoutside atmosphere, and a delaying layer (4) which regulates theconveyance of moisture from the refrigerated product to the activatorlayer and to the indicator layer. The delaying layer can also be madefrom the product packaging on which the device is placed. In this caseone can dispense with a separate delaying layer. All additional layersare not necessarily required for the correct function of the device, andso are optional. In its simplest embodiment the device according to theinvention is therefore characterised by the following layers. The layersequence specified below (starting from the side lying away from therefrigerated product) constitutes a preferred embodiment of the deviceaccording to the invention:

-   -   (a) surface layer (1);    -   (b) indicator layer (2);    -   (c) activator layer (3);    -   (d) optional delaying layer (4).

However, this layer sequence is not essential for successfulimplementation of the invention. Only the following boundary conditionswith regard to the layer sequence are to be fulfilled:

-   -   (i) The surface layer must be the furthest away from the        refrigerated product in relation to the indicator layer, the        activator layer and the delaying layer;    -   (ii) At least the indicator layer must be further away from the        refrigerated product than the optionally provided delaying        layer.

Therefore, in the case of the delaying layer being provided, theposition of the activator layer can lie between the surface layer andthe indicator layer, between the indicator layer and the delaying layer,or beneath the delaying layer. The following additional layer sequencesare thus produced in addition to the above layer sequence(1)-(2)-(3)-(4): (1)-(3)-(2)-(4) and (1)-(2)-(4)-(3).

Additional optional layers can be introduced provided this does not haveany negative impact upon the function according to the invention. Inparticular, the following additional layers can be provided:

Adhesive layers (5, 6, 7) can be added in order to guarantee thecohesion of the layer sequence. In particular, with the layer sequenceshown above it is possible

-   -   to provide an upper adhesive layer (5) directly beneath the        surface layer 1);    -   to provide a middle adhesive layer (6) between the indicator        layer (2) and the activator layer (3); and/or    -   to provide a lower adhesive layer (7) beneath the delaying layer        (4).

As an additional optional layer a separating layer (8) can be providedbetween the indicator layer (2) and the activator layer (3) so as tothus prevent direct contact of the activator and the indicator on theboundary surface between the layers and to provide another possibilityfor regulating the activation time until there is a colour change.Moreover, said separating layer (8) can simplify production of thedevice according to the invention.

Other layers are also conceivable such as e.g. separating layers betweenother layers of the device according to the invention and/or additionalindicator and/or activator layers which can, for example, bring aboutadditional colour changes under certain conditions. Likewise, it is notruled out to provide a number of the layers described here in multiples.For example, one could consider providing the layer sequences describedin this application twice or a number of times one over the other. Thistype of “sandwich structure” using two or more indicator and/oractivator layers leads to a gradual or step-by-step colour change whichmakes it possible to distinguish between short-term and longer-terminterruptions to the refrigeration chain.

Other significant embodiments of the present invention are characterisedby the following layer sequences:

-   -   (a) surface layer (1)    -   (oH) upper adhesive layer (5)    -   (b) indicator layer (2)    -   (mH) middle adhesive layer (6)    -   (c) activator layer (3)    -   (d) delaying layer (4)    -   (uH) lower adhesive layer (5)    -   and    -   (a) surface layer (1)    -   (oH) upper adhesive layer (5)    -   (b) indicator layer (2)    -   (t) separating layer (8)    -   (e) activator layer (3)    -   (d) delaying layer (4)    -   (uH) lower adhesive layer (7);

With these two layer sequences it is of course possible to leave out thelower adhesive layer (7) in each case, to leave out the upper adhesivelayer (5) in each case or to leave out both the lower and the upperadhesive layer (5, 7).

FIG. 1 shows the layer sequence according to one of the simplestembodiments of the present invention. Since no adhesive layers areprovided in this embodiment, this embodiment is an option in particularin cases in which the device according to the invention is to beintegrated into the product packaging, i.e. in which the surface layerforms a layer of the product packaging. Alternatively, the layersequence according to FIG. 1 could be held together by a stuck-onproduct label. In this connection the product label must be transparentin the region of the device according to the invention. The delayinglayer may be formed by a layer of the product packaging lying further tothe inside or may be positioned over one such layer. By integrating thedevice according to the invention into the product packaging in this waythe desired cohesion of the layers can also be guaranteed without anyadhesive layers lying in between.

With the layer sequence according to the second embodiment the cohesionof the layers and the integrity of the device is achieved by appropriateadhesive layers. This is shown in FIG. 2.

In the embodiment according to FIG. 3 the middle adhesive layer isreplaced by a separating layer (8). The cohesion of the layers isguaranteed by a broader configuration of the surface layer (1) and ofthe upper adhesive layer (5) which enables direct contact and cohesionwith the delaying layer (4) outside of the region covered by theindicator layer (2) and the activator layer (3). In the layer sequenceshown in FIG. 3 the separating layer (8) is optional, i.e. an additionalembodiment relates to the same layer sequence, but without theseparating layer.

FIG. 4a shows the layer sequence of another embodiment of the presentinvention. In this case there is only a single adhesive layer, namelythe upper adhesive layer (5) between the surface layer (1) and theindicator layer (2). The cohesion of the layers and so the integrity ofthe device are guaranteed by larger dimensions of the surface layer andof the upper adhesive layer (5). The upper adhesive layer reaching overthe indicator layer (2), the activator layer (3) and the delaying layer(4) comes into direct contact with the product packaging and forms astabile adhesive bond with the latter. This embodiment is once againshown with the optional separating layer (8).

FIG. 4b shows another version of the embodiment according to FIG. 4a .In this version the delaying layer (4) has been left out.

FIG. 4c shows another version of the embodiment according to FIG. 4a .In this version the separating layer (8) has been left out.

FIG. 5a shows another version of the embodiment according to FIG. 4a .In this version the delaying layer (4) is integrated into the productpackaging, i.e. the delaying layer (4) is formed exclusively by a layerof the product packaging. In this case the adhesive bond takes placebetween the upper adhesive layer (5) and the delaying layer (4—layer ofthe product packaging).

FIG. 5b shows another version of this embodiment. The layer sequencecorresponds to that of FIG. 5a , the indicator layer (2) and theactivator layer (3) being interchanged with one another however.

FIG. 6 shows another version of the embodiments of FIGS. 4a and 5a . Inthis version there is a separate delaying layer (4) in addition to theproduct packaging. This layer is somewhat wider than the layers lyingover it. The cohesion of the layers is guaranteed by the contact betweenthe upper adhesive layer (5) and the overlaying region of the delayinglayer (4). Moreover, the region of the adhesive layer (5) overlaying thedelaying layer (4) makes it possible to fix the device on the productpackaging (which serves as an additional delaying layer; not shown inFIG. 6).

FIG. 7 shows another version of the embodiment according to FIG. 3. Inthis version the optional separating layer (8) has been left out.Moreover, the lower adhesive layer (7) is only located in the regionsoutside of the indicator layer (2) and the activator layer (3) lyingover it. This version also allows the use of pressure-sensitiveadhesives which are non-permeable or only very slightly permeable tomoisture and water vapour.

FIG. 8 relates to an embodiment in which the activator layer (3) ispositioned beneath the delaying layer (4). In this case the activatormigrates together with the moisture through the delaying layer (4) tothe indicator layer (5).

FIGS. 9a, 9b and 9c show additional embodiments in which the activatorlayer is located at a different point: These embodiments correspond tothose of FIGS. 4a, 4b and 4c , only the indicator layer (2) and theactivator layer (3) being respectively interchanged with one another.

FIG. 10 shows an embodiment according to FIG. 7 which additionally has asecond activator layer (3) beneath the delaying layer (4) and within theregions covered by the lower adhesive layer (7). The provision of asecond activator layer offers the advantage that the colour change takesplace gradually or step by step. It is therefore preferred in cases inwhich the display is to allow a distinction to be made between short andlonger interruptions to the refrigeration chain. Of course, a secondactivator layer can also be provided at a different position of thedevice, e.g. between the indicator layer (2) and the upper adhesivelayer (5).

FIG. 11 shows another version of the embodiments according to FIGS. 4aand 9a : In the embodiment of FIG. 11 the activator layer (3) ispositioned beneath the delaying layer (4). In this layer sequence thedelaying layer (4) can act as a separating layer, and so replace theseparating layer shown in FIGS. 4a and 9 a.

FIG. 12 relates to another embodiment in which the product packagingserves as a delaying layer (4) and in which a separating layer (8) ispositioned between the indicator layer (2) and the activator layer (3).Moreover, in this embodiment the separating layer projects over theindicator layer (2) and the activator layer (3). This allows directcontact between the upper adhesive layer (5) and the separating layer(8), and this contributes to the integrity of the device. Another loweradhesive layer (7) is positioned between the separating layer (8) andthe product packaging/delaying layer (4) so that it partially or fullyencloses the activator layer (3).

FIG. 13 shows another embodiment of the device according to theinvention. In this embodiment two delaying layers (4) are provided. Afirst delaying layer (4) between the indicator layer (2) and theactivator layer (3) is formed by the product packaging. This delayinglayer (4) serves at the same time as a separating layer. A seconddelaying layer (4) is located beneath the activator layer (3). This canbe e.g. a water vapour-permeable, thin protective film as generally usedwithin food packaging. The device of this embodiment can be producedparticularly easily at the same time as the rest of the productpackaging.

The delaying layers shown in FIG. 13 are of course also used in all ofthe other devices according to the present invention if the invention isapplied to appropriately made product packaging. It is the overalldelaying effect which is caused by all of the delaying layers, includingthe product packaging, that is to be taken into consideration in eachcase.

The devices shown in FIGS. 1 to 13 (i.e. the layer sequences andadditional structural features shown) are preferred within the frameworkof the present invention. The devices shown in FIGS. 4a-c, 5a, 5b and9a-c are particularly preferred.

Surface Layer

The surface layer has the following functions:

-   -   The surface layer prevents moisture from penetrating from the        outside to the indicator layer and/or the activator layer.    -   The surface layer has sufficient transparency in order to make a        colour change in the indicator layer visible from the outside.    -   The surface layer allows additional marking of the display        device according to the invention, e.g. by applying a logo.

Any film materials which are suitable for fulfilling the requirementsspecified above can be used as the surface layer. In this connection thetwo requirements specified first are of equal priority, while thepossibility of applying a logo is of lesser importance. Therefore, anytransparent films which are non-permeable or so slightly permeable tomoisture that this has no effect upon the functional efficiency of thedevice according to the invention can be used. For example, surfacelayers through which so little moisture passes that when the deviceaccording to the invention is stored for 1 year at 25° C. and 75%relative air humidity the amount of moisture that penetrates over thisperiod of time has no effect perceivable with the naked eye upon thefunction of device can be used. This means, for example, that a filmmade of polypropylene (PP) with a thickness of 50 μm or more, preferably60 μm or more, can be used. One can also use other film materials suchas e.g. high-density polyethylene (HDPE) with comparable water vapourpermeability. With materials with low water vapour permeability it is ofcourse possible to reduce the thickness of the film accordingly.Conversely, materials with greater water vapour permeability can also beused if the film thickness is accordingly adapted. One must of courseensure that there is sufficient transparency here. Another suitable filmmaterial is polyvinylidene chloride because its water vapourpermeability is lower by approximately one order of magnitude than thatof polypropylene. One can also use biodegradable films based on starchor cellulose which also meet the requirements for transparency andmoisture impermeability.

One can of course also use surface layers which on their part arecomposed of a number of layers of different plastics (provided therequirements specified above are met by the multilayered surfacelayers).

As another alternative, the surface layer can be formed by applying aprotective paint that is impermeable to moisture. In this case theaforementioned requirements with regard to transparency and water vapourpermeability are to be imposed upon the surface layer formed fromprotective paint in the same way. The thickness of the protective paintis to be adapted accordingly. Silicons formed by polysiloxanes andpaints formed by polymeric synthetic resins are suitable materials forthe protective paint.

A combination of this protective paint and the aforementioned films isalso possible. In this case the combination thus formed must of coursemeet the above requirements with regard to transparency and water vapourpermeability.

The preferred surface layer is a polypropylene film with a thickness inthe range of 40-80 μm, preferably approx. 60 μm.

Upper Adhesive Layer

The optional upper adhesive layer can be formed by any adhesive.Preferably, pressure-sensitive adhesives are used. Appropriatepressure-sensitive adhesives are described, for example, in the standardreference “Handbook of Pressure-Sensitive Adhesive Technology” byDonatas Satas (van Nostrand, N.Y. 1989). These include in particularacrylate-, natural rubber-, synthetic rubber-, silicon- or EVA-basedpressure-sensitive adhesives. Pressure-sensitive adhesives with anatural base such as casein-, gelatine- and starch-based adhesives arepreferred. Hot-melt adhesives and flexographic printing adhesives suchas e.g. Novarad® RCL-6015 produced by Novamelt® and other UV-curableacrylate-urethane-based or acrylate-epoxy-based monomer/oligomercompositions are also conceivable.

The adhesive layer is used in a thickness of typically 5-1000 μm,preferably 10-250 μm. In particular, the aforementioned flexographicprinting adhesives are typically applied an amounts of 1-50 g/m²,preferably 5-40 g/m², more preferably 10-30 g/m².

Indicator Layer

The indicator layer is characterised by the presence of at least oneindicator. In connection with the present invention the term “indicator”relates to any substance or mixture of substances which shows a colourchange as the result of a chemical reaction or other interaction with anappropriate activator. A typical representative of these substances arethe so-called pH indicators. PH indicators show a colour change as soonas the pH value changes such that a characteristic change value for therespective pH indicator is exceeded. If, for example, the pH indicatoris blue in the alkaline medium (pH>7) and red in the acidic medium(pH>7), a colour change can take place if the medium in the indicatorlayer is alkaline and an acid is used as the activator. Likewise, it ispossible to use said pH indicator in an acidic medium and to use analkali as an activator.

Of course it is necessary to match the pH indicator, the surroundingmedium and the activator to one another so as to guarantee that thedesired colour change takes place upon migration of the activator intothe indicator layer. With pH indicators, this can take place by anappropriate choice of pH indicator (in view of the pH value at thecolour change), by setting the pH value of the indicator layer and by anappropriate choice of activator.

The pH indicators include colorants of natural origin and syntheticcolorants. Natural colorants which can, for example, be obtained fromplants such as vegetables and fruit are preferred. These include, amongother things, flavonoids such as e.g. anthocyanins. Anthocyanidins arepreferred here. The use of cyanidin is particularly preferred.Delphinidin, malvidin, peonidin and petunidin can also be mentioned.Mixtures of colorants can also be used. However, one must ensure herethat the colour change characteristics of the individual colorants arematched to one another such that a clearly perceptible colour changetakes place under the given conditions (presence of an activator andmoisture, optionally in the presence of a matrix and additionalcomponents).

In addition to pH indicators, other substances which have anactivator-induced colour change can also be used. Redox indicators canbe mentioned here in particular. These are colorants which show a colourchange upon reduction and/or oxidation. Typical examples are ferroin ormethylene blue. A comprehensive list of redox indicators can be found onthe English version of Wikipedia under the entry “Redox indicator”(September 2012 version). Accordingly, appropriate reducing agentsand/or oxidising agents can be used as activator substances.

Another class of appropriate indicators are substances which show acolour change as a result of complex formation. A simple example of thisis water-free copper sulphate CuSO₄, white, which acquires the bluecolour of the complex [Cu(H₂O)₆]SO₄ in the presence of moisture. In thissimple case the moisture itself acts as an activator so that(exceptionally) one can dispense with the activator layer. In all casesin which coloured complexes are formed with other ligands as H₂O, theligand in question serves as an activator and is provided in theactivator layer.

PH indicators and in particular the aforementioned anthocyanidins arepreferred indicator material, and cyanidin is very particularlypreferred.

In addition to the indicator substance, the indicator layer can includeadditional optional components. Appropriate additional optionalcomponents can be chosen in particular from the following components:

-   -   Matrix materials such as e.g. agar-agar, cellulose, starch, gum        arabic, guar gum, gelatine and arrowroot starch; cellulose is        preferred. Polyethylene glycol is also suitable. If the device        according to the invention is produced by the preferred printing        process, one must ensure that the viscosity of the matrix        materials used is adapted to the printing process. This can take        place by correctly choosing the chain length of the polymeric        matrix materials. It is also possible to use a homogeneous or        heterogeneous mixture of the matrix material with an appropriate        solvent with an appropriate viscosity. It is also conceivable to        use a textile fabric or fleece. If the indicator is applied to a        fabric or fleece, said fabric or fleece acts more as a carrier        than as a matrix enclosing the indicator. In these cases the        material to be used for the fabric or fleece is not subject to        any further restriction (other than that is should be inert with        respect to the indicator and the activator). An appropriate        material is for example cellulose, i.e. for example a layer of a        paper handkerchief.    -   Substances which set the medium at appropriate initial        conditions in order to guarantee stable colouring of the        indicator (before the colour change); for example, when using a        pH indicator and when using an acid as an activator the medium        with alkali such as Na₂CO₃, NaHCO₃, CaO or CaCO₃ can be set to        an alkaline pH value; setting to an acidic pH value can take        place with acids such as e.g. lactic, oxalic, tartaric and        citric acid;    -   Hygroscopic materials including hygroscopic polymers such as        e.g. acrylic acid acrylate polymers and hygroscopic salts such        as e.g. magnesium chloride, potassium chloride and calcium        chloride which may affect (e.g. accelerate) the colour change;    -   Salts for lowering the melting point of water. The use of salts        for lowering the melting point of water is a possibility if the        device according to the invention is to be used with        refrigerated products containing salt (e.g. pretzels). Due to        the presence of salt in the indicator layer (and in the layers        of the device according to the invention lying further to the        inside), the device according to the invention can already be        activated at temperatures below 0° C. at which the refrigerated        product also starts to defrost. Since the lowering of the        melting point is a colligative phenomenon, any salts can be        used. Non-toxic salts such as e.g. NaCl are preferred.    -   Stabilisers, such as e.g. potassium sorbate for suppressing        mould; additional preserving agents comprise calcium chloride        and ethanol; the use of such stabilisers is preferred in        particular when using natural colorants.

The amount of indicator colorant to be applied is typically in the rangeof from 0.1 to 100 g/m², preferably from 1 to 40 g/m², particularlypreferably from 4 to 12 g/m². The amount of indicator applied affectsthe speed and intensity of the colour change. Moreover, heavyapplication of colour (i.e. applied amounts in the upper half of theranges specified above) facilitates perceptibility of the colour change.On the other hand, heavy application of colour can make drying difficultwithin the framework of the production process. It has proven to beadvantageous to apply a number of thin layers instead of one heavyindicator layer and to allow this to dry before each subsequentindicator layer is applied. For example, 2-40 layers can be applied.4-10 layers are preferred, and 6-8 layers are more preferable. The easeof drying is of course also dependent upon the composition of the pHindicator layer (e.g. hygroscopic properties of the components and watercontent). By appropriate setting of the water content, choice of matrixmaterial and application amount for each layer a desired drying speedcan be set. By using printing machines the applied amount of indicatorcan be matched to the carrying capacity of the printing machine.

Middle Adhesive Layer

The details given in section 5.5 for the upper adhesive layer apply inthe same way to the middle adhesive layer. However, in the middleadhesive layer care must be taken to ensure that sufficient moistureconveyance from the refrigerated product to the indicator layer isguaranteed.

The desired suitability for moisture conveyance can on the one hand beachieved by choosing appropriate bonding agents/adhesives. Adhesiveswhich are capable of allowing the passage of moisture are in particularstarch- or gelatine-based adhesives. By reducing the amount applied themoisture permeability of additional adhesives, which in their own righthave lower moisture permeability (in relation to the same applicationamounts), can be brought to an acceptable level. Thus, with appropriateadaptation of the application amount, a plurality of additionaladhesives can be used.

On the other hand it is possible to provide pores or openings in themiddle adhesive layer in which there is no adhesive and by means ofwhich the moisture can migrate, without hindrance, into the indicatorlayer. The form and size of the openings are not specified any moreprecisely provided that the overall surface of the openings issufficient in order to guarantee the conveyance of moisture necessaryfor the desired colour change.

Separating Layer

The provision of a separating layer between the indicator layer and theactivator layer is particularly recommended if the device according tothe invention is to be produced by applying from layer to layer.

In this case, if the separating layer is missing, direct coating of theactivator layer by the (still moist) material of the indicator layercould lead to a colour reaction on the boundary surface before theindicator layer has sufficiently dried. In order to avoid this prematureboundary surface reaction, the indicator layer and the activator layercan be separated from one another by said separating layer and so thepremature colour reaction can be avoided.

The separating layer must be capable of absorbing and storing smallamounts of moisture without passing these on to the adjacent layerbefore the subsequent drying stage.

The separating layer must be dry before applying the subsequent layer.This means that the separating layer must, if applicable, be dried. Theseparating layer can also be applied in the form of a number of separatelayers.

By appropriately choosing the adhesive, the aforementioned middleadhesive layer can act as a separating layer. Alternatively, syntheticfilms with appropriate moisture permeability could be used. Likewise,the use of a layer formed from starch is conceivable. Separating layersformed from gelatine or paper (cellulose) are particularly preferred.The use of a fabric or fleece is also possible. In this case too thematerial to be used for the fabric or fleece is not subject to anyfurther restriction (other than that it is to be inert with respect tothe indicator and the activator). Cellulose is preferred. Othermaterials suitable for the separating layer are waxes and in particularlow-melting (<25° C.) waxes, greases and in particular low-melting (<25°C.) greases, polyethylene glycol, dextrin, casein, starch, polyvinylalcohol, gelatine, polysaccharides such as agar-agar or pectin, andmixtures of the latter.

Activator Layer

The activator is chosen such that a chemical reaction or otherinteraction with the indicator leads to a colour change. When using pHindicators the activator is either an acid or an alkali. When choosingan acid, the medium of the indicator layer must be alkaline (or at leastmore alkaline than the pH transition point of the indicator). In thesame way, when using an alkali as the activator, the medium of theindicator layer must be acidic (or at least more acidic than the pHtransition point of the indicator).

Preferred acids are oxalic acid, lactic acid and tartaric acid. Citricacid is particularly preferred. When using alkalis as the activator,Na₂CO₃, NaHCO₃, CaO or CaCO₃ can once again be used.

If redox indicators are used, what has been said about pH indicatorsapplies in the same way. This means that oxidising agents can be used asactivators provided the redox indicator is in the reduced state. In thiscase a reduced medium in the indicator layer can stabilise the redoxindicator. Conversely, it is possible to use a reducing agent as anactivator provided the redox indicator is in the oxidised form. In thiscase an oxidised medium in the indicator layer can stabilise the redoxindicator.

Suitable oxidising agents include organic percarboxylic acids and metalsalts such as MnO₂; suitable reducing agents include ascorbic acid,sulphite salts and tin(II) salts. When choosing appropriate oxidisingagents and reducing agents, one must ensure that there is sufficientstability under the given conditions, i.e. no reaction with the othercomponents of the activator layer is to take place over the plannedstorage period. If the device is used for food, care must be taken toensure, moreover, that no health risk arises from the oxidising and/orreducing agents used.

These substances are suitable both for use as the activator and for usefor the desired setting of the medium of the indicator layer.

Other components of the activator layer are optional. For example, thematrix materials specified for the indicator layer can be used. In thiscase too fabrics or fleeces can be used. Once again, the material to beused for the fabric or fleece is not subject to any further restriction(other than that it is to be inert with respect to the indicator and theactivator). Cellulose is preferred.

In addition, a colorant can be incorporated into the activator layer.Suitable colorants are for example titanium dioxide or food-safecolorants. As a result of the colouring of the activator layer, e.g.with titanium dioxide, the contrast with the colour change in theindicator layer can be increased.

Furthermore, it can be advantageous to incorporate hygroscopic materialssuch as hygroscopic polymers (e.g. acrylic acid acrylate polymers) orhygroscopic salts (e.g. magnesium chloride, potassium chloride andcalcium chloride) into the activator layer.

The amount of activator in the activator layer is typically 0.1 to 100g/m², preferably 1 to 40 g/m², particularly preferably 4 to 12 g/m². Inthis case too it is advantageous to form the activator layer byseparately applying and drying a number of individual layers so as tothus facilitate the drying. 2-30 individual layers can be used.Activator layers which are formed from 3-8 individual layers arepreferred, and 4-6 individual layers are more preferable.

Delaying Layer

The delaying layer forms a type of “moisture buffer” that absorbs acertain amount of moisture before the latter is passed onto theactivator layer. The advantage of this is that no colour change takesplace as a result of the release of very small amounts of moisture. Inthis way false positive displays can be avoided, e.g. when the indicatoris touched by the consumer.

The delaying layer is an optional component of the device according tothe invention. The delaying effect required for successfulimplementation of the invention can also be achieved by other layers ofthe device according to the invention such as e.g. separating oradhesive layers. The delaying effect caused by the product packaging isalso to be taken into account.

The period of time from the first formation of moisture to the colourchange can thus be set by appropriately choosing the layers causing thedelay (in relation to presence or absence, materials used and theirthickness), taking into account the delaying effect of the productpackaging. Critical for this period of time is the overall delayingeffect of all of the layers between the product and the outermost layerrelevant to the colour effect (i.e. the activator or indicator layer).

The materials that can be used for the delaying layer correspond to thematerials specified under point 5.8 for the separating layer such ase.g. waxes, greases, polyethylene glycol, dextrin, etc. In other words,films with sufficient moisture permeability can be used, a layer formedfrom starch or, more preferably, a layer formed from gelatine.Particularly preferred is the use of paper or cardboard (i.e. a layer ofcellulose), e.g. paper with a thickness of 25-80 g/m². When using paper,newspaper or paper with a comparable thickness of approx. 40-60 g/m², inparticular 50 g/m², has proven to be advantageous. If a shorter changetime is desired, the use of tissue paper or paper with a comparablethickness of approx. 20-30 g/m², in particular 25 g/m² has proven to beadvantageous.

The use of paper or cardboard is particularly preferred in cases inwhich the indicator layer and the activator layer are to be laminatedonto one another. In these cases the delaying layer, in addition toachieving the desired delaying effect, can also serve as a carriermaterial for the (indicator or activator) layer which is located closerto the refrigerated product.

As already mentioned, when choosing an appropriate delaying layer themoisture permeability of the other layers of the device up to andincluding the outermost colouring layer (i.e. the indicator or activatorlayer) and the product packaging lying beneath are advantageously alsoto be taken into consideration: If one of the other layers and/or theproduct packaging has low moisture permeability, the moisturepermeability of the delaying layer should be as high as possible (or thedelaying layer is completely left out if maximum permeability isrequired—see below), If, however, the moisture permeability of the otherlayers and the product packaging is high, a delaying layer should beused which lies in the lower region of the range specified above so asto thus set the desired period of time until the colour changes.

Another configuration of the present invention consists of using onlythe packaging of the refrigerated product (or a layer of the latter) asthe delaying layer, i.e. leaving out the delaying layer as a componentpart of the device according to the invention. This embodiment isparticularly suitable for use with product packaging which already has asufficiently great delaying effect and/or in devices in which the otherlayers provided (such as e.g. adhesive and/or separating layers) providea sufficient delay in combination with the product packaging. Here, ofcourse, the same requirements are made of the product packaging, i.e.the packaging material (or its component part) must be capable ofabsorbing moisture and releasing it again with an appropriate delay.Packaging made of cardboard is very suitable for this purpose. If,however, the packaging is coated with a material that is impermeable tomoisture, it must be guaranteed that this moisture-impermeable materialis not present, or is at least provided with pores, in the region inwhich the device according to the invention is applied. Alternatively,said moisture-impermeable material can be applied only after the deviceaccording to the invention has been positioned so that the conveyance ofmoisture through the packaging of the device according to the inventiontakes place beneath the moisture-impermeable layer and is not hinderedby the latter.

Lower Adhesive Layer

The details given with regard to the middle adhesive layer under point5.7 apply in the same way to the lower adhesive layer. Here too one mustensure that there is sufficient conveyance of moisture by takingappropriate measures (i.e. by choosing an appropriate adhesive and/orproviding openings).

Setting the Period of Time Until there is a Colour Change

The desired period of time between the start of the defrosting processand the colour change of the device according to the invention(hereinafter: “change time”) is in the range of a few minutes to anumber of hours, in particular 10 mins to 5 hrs, preferably 30 mins to 4hrs, more preferably 1 hr to 3 hrs and in particular approximately 2hrs.

Depending on the type of product group, it can be advantageous todevelop devices according to the invention with a fast colour changespeed, an average colour change speed or a slow colour change speed.Thus, a device with fast colour change should only change colour afterapprox. 60 minutes (e.g. in the range of 60 to 100 minutes). A devicewith average colour change speed should only change colour after approx.90 minutes (e.g. in the range of 90 to 140 minutes). A device with slowcolour change should only change colour after approx. 140 minutes (e.g.in the range of 140 to 200 minutes). These specified change times relaterespectively to the standard test conditions according to section 5.1above.

By means of the following repetitive process the period of time betweenthe start of the defrosting process and the colour change of the deviceaccording to the invention can be set at the desired value:

-   -   1. In a first step a basic device according to the present        description is produced. One can produce any of the devices        according to the exemplary embodiments described below.    -   2. Next, the basic device is placed over the product packaging        of the refrigerated product in question. The change time is        determined as defrosting starts.    -   3. If the change time determined is longer than the specified        target value, step 4 below is carried out; if the determined        change time is shorter than the specified target value, step 5        below is carried out; otherwise there is no further need for        adaptation, and the process is completed with step 8.    -   4. The current device (in the first round: basic device) is        reworked in modified form so that the overall delaying effect of        all of the relevant layers of the device is reduced when        conveying moisture. This takes place by using one or a number of        materials better suited to the conveyance of moisture in at        least one relevant layer and/or the layer thickness of at least        one relevant layer is reduced. The device thus obtained is        tested according to step 6 below.    -   5. The current device (in the first round: basic device) is        reworked in modified form so that the overall delaying effect of        all of the relevant layers of the device is increased when        conveying moisture. This takes place by using one or a number of        materials less well suited to the conveyance of moisture in at        least one relevant layer and/or the layer thickness of at least        one relevant layer is increased. The device thus obtained is        tested according to step 6 below.    -   6. Next the modified device is placed over the product packaging        of the refrigerated product in question. The change time is        determined as defrosting starts.    -   7. If the change time determined is longer than the specified        target value, step 4 above is carried out; if the determined        change time is shorter than the specified target value, step 5        above is carried out; otherwise the process is completed with        step 8.    -   8. The last tested device meets the requirement; there is no        longer any need for modification.

According to a preferred embodiment the delaying effect of one or anumber of layers is adapted by using polyethylene glycol as the matrixmaterial (e.g. in the indicator layer, separating layer and/or activatorlayer). Here the delaying effect can be set as desired, in particular bychanging the chain length (i.e. molar mass) of the polyethylene glycoland/or of the mixture ratio of PEG molecules of different molar masses.Appropriate molar masses are in the range of 600 to 4000 g/mol,preferably in the range of 800 to 1500 g/mol. When using mixtures liquidpolyethylene glycols with a molar mass of below 600 g/mol can also beused.

In the same way, the delaying effect can also be adapted by adapting themolecular weight of other polymeric matrix components such as polyvinylalcohol.

Production

The device according to the invention can be produced by any methods inwhich the layers in question are formed or provided and can be broughtinto contact with the respectively adjacent layers. Here, neither thesequence of individual procedural steps (provision or formation of therespective layer and bringing into contact with the adjacent layer orlayers) nor the techniques used for forming the layers are specified.However, the following procedures have proven to be advantageous.

Version (I):

-   -   (A-1) Provision of the surface layer (a),    -   (A-2) Coating of the surface layer (a) with the indicator layer        (b),    -   (A-3) Optionally, drying of the indicator layer (b) to produce        an arrangement (A)    -   (B-1) Provision of a delaying layer (d)    -   (B-2) Coating of the delaying layer (d) with the activator layer        (c    -   (B-3) Optionally, drying of the activator layer (c), to produce        an arrangement (A)    -   (C) Laminating the arrangements (A) and (B).

The chronological sequence of implementing steps (A-1) to (A-3) inrelation to steps (B-1) to (B-3) is not specified in any more detail.

Any additional layers provided, such as separating or adhesive layers,are introduced at an appropriate point by carrying out the followingadditional steps:

-   -   (X-1) Coating of the already formed or provided adjacent layer        with the appropriate material so as to form the additional layer        to be applied;    -   (X-2) Optionally, drying of the additional layer to be applied.

If, for example, an additional adhesive layer is to be introducedbetween the surface layer and the indicator layer, the aforementionedsteps (X-1) and (X-2) are carried out between steps (A-1) and (A-2). If,however, an adhesive layer is to be provided beneath the delaying layer(d), the respective steps (X-1) and (X-2) can be carried out before step(B-1) or at any later point in time.

Version (II):

Here all of the layers are applied sequentially (i.e. after providing orapplying and drying the respectively preceding layer). In order to avoida premature colour reaction on the boundary surface between theindicator layer and the activator layer, in this version a separatinglayer is provided between these two layers.

The sequence of applying the individual layers is determined by thedesired sequence of layers in the device to be produced. However, it ispossible to invert the sequence of applying the individual layers, i.e.as a first step the surface layer (a) or the delaying layer (d) can beprovided. The following procedures are thus produced for an exemplarylayer sequence:

-   -   (D-1) Provision of the surface layer (a),    -   (D-2) Coating of the surface layer (a) with the indicator layer        (b),    -   (D-3) Optionally, drying of the indicator layer (b)    -   (D-4) Coating of the indicator layer (b) with the separating        layer (t),    -   (D-5) Optionally, drying of the separating layer (t),    -   (D-6) Coating of the separating layer (t) with the activator        layer (c),    -   (D-7) Optionally, drying of the activator layer (c),    -   (D-8) Coating of the activator layer (c) with the delaying layer        (d),    -   (D-9) Optionally, drying of the delaying layer (d);        and    -   (D′-1) Provision of the delaying layer (d),    -   (D′-2) Coating of the delaying layer (d) with the activator        layer (c),    -   (D′-3) Optionally, drying of the activator layer (c)    -   (D′-4) Coating of the activator layer (c) with the separating        layer (t),    -   (D′-5) Optionally, drying of the separating layer (t),    -   (D′-6) Coating of the separating layer (t) with the indicator        layer (b),    -   (D′-7) Optionally, drying of the indicator layer (b),    -   (D′-8) Coating of the indicator layer (b) with the surface layer        (a),    -   (D′-9) Optionally, drying of the surface layer (a).

In these method versions too, any additional layers provided, such asadditional separating or adhesive layers, can be introduced at anappropriate point by carrying out the additional steps (X-1) and (X-2)described above.

In alternative layer sequences according to FIGS. 1 to 13 the sequenceof applying the individual layers changes accordingly. Thus, in thesemethods, any layers can of course also be left out. According to onepreferred version of the methods described above, no separating layer isapplied. Steps D-4 and D5 or D′-4 and D′-5 are also left out. In thiscase it is essential to avoid a premature colour reaction between theactivator and the indicator during production. This can be achieved byusing a highly volatile solvent in the printing process. Suitable highlyvolatile solvents are in particular organic solvents that have a vapourpressure that is higher than the vapour pressure of water (respectivelyat 20° C.) and/or with which the boiling point is lower than with water.They include ethanol, acetone, diethyl ether, methanol, isopropanol,ethyl acetate and methyl acetate as well as mixtures of such solvents.Ethanol is preferred. The printing process is carried out layer bylayer, as above. It is very advantageous that the second printed layerrelevant to the colour formation is dried as quickly as possible afterapplication. In the methods described above this means that steps D6 andD7 are carried out almost simultaneously and directly after step D-3 (orthat steps D′-6 and D′-7 are carried out almost simultaneously anddirectly after step D′-3). The immediate drying can be achieved bygenerating a gas flow, preferably an air flow, over the printed surface.The highly volatile solvent is discharged by the gas flow beforeundesired migration of the activator into the indicator layer takesplace.

The layers can be applied by any technology which is suitable for theformation of thin layers. Printing machines which are capable ofapplying a number of material layers one after the other and ofrespectively drying them directly after application have proven to beparticularly suitable. Printing machines, for example, which workaccording to the offset, flexographic or screen printing processes aresuitable. Other methods for applying thin layers include sprayingprocesses, doctor blade application processes, dipping processes etc.

The compositions to be applied for every material layer are adapted asregards their viscosity to the requirements of the chosen (printing)process. Appropriate thickening agents can be used for this purpose. Allthickening agents which are inert with respect to the indicator and theactivator and which do not hinder the desired conveyance from theactivator to the indicator are suitable. Polysaccharides such as pectin,xanthan, guar gum, agar-agar, cellulose and cellulose derivatives aswell as calcium acetate and glycerine can be mentioned as examples. Thedesired viscosity can also take place by suitable adaptation of theconcentration of the materials in the chosen solvent. If an additionalincrease of the concentration is desired, the production of the solutioncan also take place at an increased temperature. It is thus possible,for example, to obtain a highly concentrated solution of citric acid inwater by producing a saturated solution at approx. 50° C. to 60° C. Inthis embodiment the application of the materials can also take place atan increased temperature in order to prevent premature solidification orcrystallisation of individual components.

However, when using spraying processes it is not necessary to increasethe viscosity of the solution to be sprayed on, e.g. by addingthickening agents.

The drying of the individual applied layers (and also the dry storage ofthe device produced) is important in order to prevent a premature colourchange. The degree of drying must be appropriately chosen in order tofulfil this requirement. As already mentioned in sections 5.6 and 5.9,it may be advantageous for acceleration of the drying to form one ormore of the layers of the device according to the invention byrespectively applying a plurality of thin layers with the samecomposition, each last applied layer being dried before applying thenext layer. As mentioned above, the drying can be accelerated by a gasflow, preferably an air flow.

If so desired, individual drying steps can nevertheless be cut short orcompletely avoided provided it is guaranteed that at the moment at whichthe activator layer and the indicator layer are brought into contact(possibly by means of an adhesive or separating layer), the degree ofdrying is sufficiently high in order to prevent a colour change. Ofcourse drying is not required if a (sufficiently dry) pre-produced filmor layer is applied to the already existing layer or layers.

In the embodiments of the present invention, in which the deviceaccording to the invention is integrated into the packaging of therefrigerated product (e.g. by using the packaging material as a delayinglayer), production takes place in the same way, version (II)advantageously being chosen and the layer structure starting with thedelaying layer. Alternatively, the layer structure could start,according to version (II), from the surface layer and end before thedelaying layer, e.g. with the formation of the activator layer. Theintermediate product thus produced can then be applied to the packaging.Another possibility consists of proceeding according to version (I) andproducing arrangement (A) as described above.

When producing arrangement (B) the activator layer and optionallyadditional layers are applied directly to the packaging. Arrangements(A) and (B) are then laminated.

Applications

The device according to the invention is suitable for the monitoring ofthe previous thermal history of any products which have to bepermanently refrigerated. Deep frozen foods first and foremost areconsidered here. Furthermore, the device according to the invention isalso suitable, however, for use in connection with other products whichhave to be permanently refrigerated or deep-frozen. The product to berefrigerated should contain moisture, however, in order to guaranteecorrect functioning of the device according to the invention.

The practical application logically takes place by placing the deviceaccording to the invention over the outer packaging of the product to berefrigerated. Good perceptibility of the colour change can thus beguaranteed. One must of course ensure here that moisture can pass frominside the packaging to the device according to the invention as soon asthe refrigeration chain is broken.

One essential advantage of the present invention is that a reliabledisplay takes place, independently of whether there is direct contactbetween the refrigerated product and the display device. Therefore, thedevice according to the invention can be applied at any point of thepackaging. The size of the area covered by the device according to theinvention is not specified any more precisely. With regard to the goodperceptibility of the colour change, this area should howeveradvantageously not be less than 0.2 cm², preferably 0.5 cm², morepreferably 0.8 cm².

The application of a logo, additional lettering or instructions isconceivable in connection with the applications of the present inventionand is also advantageous in order to draw the consumer's attention tothe invention. A logo, lettering etc. can be applied to the deviceaccording to the invention. In this connection one should, however,ensure that the logo, lettering etc. are applied such that the colourchange can be reliably seen. One should avoid covering the whole of thedevice according to the invention with e.g. a logo. Of course, withinthe framework of the present invention it is also possible to apply alogo, lettering etc. to the packaging as well as to the device accordingto the invention.

Preferred Embodiments

One prefers the present invention using the features, components and/ormeasures which are specified above as examples and/or are identified as“preferred”. More preferred are the embodiments of the present inventionwherein two or more of the features, components and/or measuresspecified as examples and/or identified as “preferred” are combined withone another.

Particularly preferred are:

-   -   (i) the use of the materials specified as examples and/or        identified as “preferred” for the surface layer in devices which        have a layer sequence according to FIGS. 1 to 13;    -   (ii) the use of the materials specified as examples and/or        identified as “preferred” for the indicator layer in devices        which have a layer sequence according to FIGS. 1 to 13;    -   (iii) the use of the materials specified as examples and/or        identified as “preferred” for the activator layer in devices        which have a layer sequence according to FIGS. 1 to 13;    -   (iv) the use of the materials specified as examples and/or        identified as “preferred” for the delaying layer in devices        which have a layer sequence according to FIGS. 1 to 13;    -   (v) the use of the materials specified as examples and/or        identified as “preferred” for the adhesive layers in devices        which have a layer sequence according to FIGS. 1 to 13;    -   (vi) the use of the materials specified as examples and/or        identified as “preferred” for the separating layer in devices        which have a layer sequence according to FIGS. 1 to 13;    -   (vii) the use of the materials specified as examples and/or        identified as “preferred” for the surface layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the indicator layer;    -   (viii) the use of the materials specified as examples and/or        identified as “preferred” for the surface layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the activator layer;    -   (ix) the use of the materials specified as examples and/or        identified as “preferred” for the surface layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the delaying layer;    -   (x) the use of the materials specified as examples and/or        identified as “preferred” for the surface layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the adhesive layers;    -   (xi) the use of the materials specified as examples and/or        identified as “preferred” for the surface layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the separating layer;    -   (xii) the use of the materials specified as examples and/or        identified as “preferred” for the indicator layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the activator layer, wherein one        must additionally note that the indicator and the activator (as        well as the medium, for example in relation to its pH) must be        matched to one another;    -   (xiii) the use of the materials specified as examples and/or        identified as “preferred” for the indicator layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the delaying layer;    -   (xiv) the use of the materials specified as examples and/or        identified as “preferred” for the indicator layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the adhesive layers;    -   (xv) the use of the materials specified as examples and/or        identified as “preferred” for the indicator layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the separating layer;    -   (xvi) the use of the materials specified as examples and/or        identified as “preferred” for the activator layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the delaying layer;    -   (xvii) the use of the materials specified as examples and/or        identified as “preferred” for the activator layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the adhesive layers;    -   (xviii) the use of the materials specified as examples and/or        identified as “preferred” for the activator layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the separating layer;    -   (xix) the use of the materials specified as examples and/or        identified as “preferred” for the delaying layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the adhesive layers;    -   (xx) the use of the materials specified as examples and/or        identified as “preferred” for the delaying layer in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the separating layer; and    -   (xxi) the use of the materials specified as examples and/or        identified as “preferred” for the adhesive layers in combination        with the use of the materials specified as examples and/or        identified as “preferred” for the separating layer.

More preferred are those devices according to the invention wherein thepreferred combinations specified above are further combined, i.e.devices with feature combinations (i)-(ii), (i)-(iii), (i)-(iv),(i)-(v), (i)-(vi), (i)-(vii), (i)-(viii), (i)-(ix), (i)-(x), (i)-(xi),(i)-(xii), (i)-(xii), (i)-(xiv), (i)-(xv), (i)-(xvi), (i)-(xvii),(i)-(xviii), (i)-(xix), (i)-(xx), (i)-(xxi), (ii)-(iii), (ii)-(iv),(ii)-(v), (ii)-(vi), (ii)-(vii), (ii)-(viii) (ii)-(ix), (ii)-(x),(ii)-(xi), (ii)-(xii), (ii)-(xiii), (ii)-(xiv), (ii)-(xv), (ii)-(xvi),(ii)-(xvii), (ii)-(xviii), (ii)-(xvix), (ii)-(xx), (ii)-(xxi),(iii)-(iv), (iii)-(v), (iii)-(vi), (iii)-(vii), (iii)-(viii),(iii)-(ix), (iii)-(x), (iii)-(xi), (iii)-(xii), (iii)-(xiii),(iii)-(xiv), (iii)-(xv), (iii)-(xvi), (iii)-(xvii), (iii)-(xviii),(iii)-(xix), (iii)-(xx), (iii)-(xxi), (iv)-(v), (iv)-(vi), (iv)-(vii),(iv)-(viii), (iv)-(ix), (iv)-(x), (iv)-(xi), (iv)-(xii), (iv)-(xiii),(iv)-(xiv), (iv)-(xv), (iv)-(xvi), (iv)-(xvii), (iv)-(xviii),(iv)-(xix), (iv)-(xx), (iv)-(xxi), (v)-(vi), (v)-(vii), (v)-(viii),(v)-(ix), (v)-(x), (v)-(xi), (v)-(xi), (v)-(xii), (v)-(xiv), (v)-(xv),(v)-(xvi), (v)-(xvii), (v)-(xviii), (v)-(xix), (v)-(xx), (v)-(xxi),(vi)-(vii), (vi)-(viii), (vi)-(ix), (vi)-(x) (vi)-(xi), (vi)-(xii),(vi)-(xiii), (vi)-(xiv), (vi)-(xv), (vi)-(xvi), (vi)-(xvii),(vi)-(xviii), (vi)-(xix), (vi)-(xx) (vi-xxi), (vii)-(viii), (vii)-(ix),(vii)-(x), (vi)-(xi), (vi)-(xii), (vii)-(xiii), (vii)-(xiv), (vii)-(xv),(vii)-(xvi), (vii)-(xvii), (vii)-(xix), (vii)-(xx), (vii)-(xxi),(viii)-(ix), (viii)-(x), (viii)-(xi), (viii)-(xii), (viii)-(viii)-(xiv),(viii)-(xv), (viii)-(xvi), (viii)-(xvii), (viii)-(xviii), (viii)-(xix),(viii)-(xx), (viii)-(xxi), (ix)-(x), (ix)-(xi), (ix)-(xii), (ix)-(xii),(ix)-(xiv), (ix)-(xv), (x)-(xvi), (ix)-(xvii), (ix)-(xviii), (ix)-(xix),(ix)-(xx), (ix)-(xxi), (x)-(xi), (x)-(xii), (x)-(xii), (x)-(xiv),(x)-(xv), (x)-(xvi), (x)-(xvii), (x)-(xviii), (x)-(xix), (x)-(xx),(x)-(xxi), (xi)-(xii), (xi)-(xiii), (xi)-(xiv), (xi)-(xv), (xi)-(xvi),(xi)-(xvii), (xi)-(xviii), (xi)-(xix), (xi)-(xx), (xi)-(xxi),(xii)-(xiii), (xii)-(xiv), (xii)-(xv), (xii)-(xvi), (xii)-(xvii),(xii)-(xviii), (xii)-(xix), (xii)-(xx), (xii)-(xxi), (xiii)-(xiv),(xiii)-(xv), (xiii)-(xvi), (xiii)-(xvii), (xiii)-(xviii), (xiii)-(xix),(xiii)-(xx), (xiii)-(xxi), (xiv)-(xv), (xiv)-(xvi), (xiv)-(xvii),(xiv)-(xviii), (xiv)-(xix), (xiv)-(xx), (xiv)-(xxi), (xv)-(xvi),(xv)-(xvii), (xv)-(xviii), (xv)-(xix), (xv)-(xx), (xv)-(xxi),(xvi)-(xvii), (xvi)-(xviii), (xvi)-(xix), (xvi)-(xx), (xvi)-(xxi),(xvii)-(xviii), (xvii)-(xix), (xvii)-(xx), (xvii)-(xxi), (xviii)-(xix),(xviii)-(xx), (xviii)-(xxi), (xix)-(xx), (xix)-(xxi) und (and)(xx)-(xxi). Combinations of these combinations listed above are evenmore preferred.

With regard to the production methods according to the invention, themethods specified above in section 5.13, which lead to the preferreddevices according to the invention, are particularly preferred. Methodsusing printing machines are also preferred, particularly when they leadto the preferred devices according to the invention.

With regard to the industrial production of the devices according to theinvention, the following embodiments, for example, are particularlypreferred:

A preferred version has the following layer sequence:

-   -   surface layer—optional adhesive layer—indicator layer—activator        layer.

These layers may be applied over the adhesive layer on the productpackaging serving as a delaying layer (with the adhesive layerpreferably to the side of the indicator and the activator layer). Asimilar layer sequence is shown in FIG. 5a , but additionally with aseparating layer. According to the preferred version described here theseparating layer is avoided by appropriate production methods. This typeof appropriate production can take place using an industrial printingprocess (e.g. flexographic printing). In this connection the surfacelayer is first of all printed with the indicator layer, followed byfurther printing with the activator layer. In order to avoid a prematurecolour change, in this case appropriate measures must be taken so thatthe activator layer dries so quickly directly after application that nosignificant migration into the activator layer takes place. As describedabove, this can take place by using a highly volatile solvent. Thedevice obtained in this way can be mounted, e.g. on silicon paper. In aseparate procedural step (which may also be spatially and/or temporallyseparate) it is stuck onto the product packaging. In this connection ananthocyanidin colorant is preferably used as the indicator, and citricacid, lactic or tartaric acid as the activator. The aforementionedembodiment is very particularly preferred when using a cyanidin colorantas the indicator in conjunction with citric acid as the activator.

Another preferred version has the following layer sequence:

-   -   surface layer—optional adhesive layer—indicator layer—separating        layer—activator layer.

These layers may be applied over the adhesive layer on the productpackaging serving as a delaying layer (with the adhesive layerpreferably to the side of the indicator and the activator layer). Onesuch layer sequence is shown in FIG. 5a . In this version it isparticularly preferred to print a paper serving as a separating layer onone side with the indicator layer and on the other side with theactivator layer. The intermediate product obtained in this way can bedie cut in the appropriate format and stuck onto a surface layerprovided with an adhesive layer. The device obtained in this way can bemounted, e.g. on silicon paper. In a separate procedural step (which mayalso be spatially and/or temporally separate) it is stuck onto theproduct packaging. In this connection too, an anthocyanidin colorant ispreferably used as the indicator, and citric acid, lactic or tartaricacid as the activator. The aforementioned embodiment is veryparticularly preferred when using a cyanidin colorant as the indicatorin conjunction with citric acid as the activator.

The preferred uses and applications according to the invention of thepresent invention are in particular the uses and applications specifiedabove in section 5.14 which include the use of the preferred devicesaccording to the invention.

EXAMPLES Example 1

A device according to the invention according to production version I isproduced by a flexographic printing process. The layer structurecorresponds to the layer sequence shown in FIG. 9 c.

The surface layer is formed from a “PP Clear TC50 P” PP film made by thecompany UPM Raflatac®. This PP film is already provided with an adhesivelayer at the factory. Therefore, the adhesive layer over an acrylatebase “SP38” also originates from UPM Raflatac®.

The activator layer is formed over the adhesive from citric acid in acellulose matrix. The application thickness is 6 g/m². The layer isapplied using the printing process in the form of an aqueous dispersionwith a cellulose content of approx. 5% by weight and a citric acidcontent of approx. 1% by weight and is dried immediately afterwards.

Cyanidin in a cellulose matrix is used as the indicator. The indicatorlayer is applied to tissue paper with a thickness of 25 g/m² as adelaying layer. The application thickness is 6 g/m². In this case toothe layer is applied in the form of an aqueous dispersion in which thecellulose content is 5% by weight and the cyanidin content is 1% byweight. The layer is dried immediately after application.

Next, the activator layer and the indicator layer are laminated onto oneanother.

A colour change can be seen between the first defrosting of therefrigerated product (300 g deep frozen peas, temperature increase from−18° C. to 20° C.) after 150 minutes.

Example 2

A device according to the invention is produced in the same way asExample 1, the difference being that 50 g/m² thick newspaper is used.

In this example a colour change was observed under identical testconditions after 200 minutes.

The invention claimed is:
 1. A device for indicating breaks in therefrigeration chain of a frozen product, comprising the followinglayers: (a) a surface layer (1) impermeable to moisture; (b) anindicator layer (2) comprising at least one indicator; and (c) anactivator layer (3) comprising at least one activator, wherein thesurface layer is positioned over the indicator layer and the activatorlayer, wherein the surface layer prevents moisture from penetrating fromthe outside to the indicator layer and/or the activator layer, whereinthe device does not comprise a moisture reservoir, and wherein thedevice is configured such that, when applied to an upper surface of apackaging surrounding the frozen product, the surface layer in thedevice is the furthest away from the frozen product packaging, and, uponsufficient heating of the frozen product to above a freezing point ofthe frozen product, moisture originating from the frozen productpenetrates into the device through the frozen product packaging and frombelow the device and migrates upwardly from the product packagingthrough the device towards the surface layer, thereby mobilizing theindicator and/or activator to bring components of the indicator layerand the activator layer together.
 2. The device according to claim 1,wherein the indicator layer comprises a pH indicator, and the activatorlayer comprises an acid or an alkali as the activator.
 3. The deviceaccording to claim 1, wherein the indicator layer and/or the activatorlayer comprise a matrix material selected from at least one of thefollowing: agar-agar, carrageenan, gelatine, starch, gum arabic,cellulose, arrowroot starch, guar gum and polyethylene glycol.
 4. Thedevice according to claim 1, wherein the indicator layer and/or theactivator layer comprise at least one hygroscopic salt.
 5. The deviceaccording to claim 1, wherein the activator layer (c) is formed from2-30 sequential individual layers.
 6. The device according to claim 1,wherein the indicator layer (b) is formed from 2-40 sequentialindividual layers.
 7. The device according to claim 1, wherein thelayers (a), (b), and (c) are arranged as follows: (a) surface layer (1),(b) indicator layer (2), and (c) activator layer (3); or (a) surfacelayer (1), (c) activator layer (3), and (b) indicator layer (2).
 8. Thedevice according to claim 1, wherein the device is applied to packagingof a product.
 9. The device according to claim 8, wherein the product isrefrigerated and wherein a period of time between first defrosting ofthe product and color change of the indicator is in the range of 0.5hours to 3 hours.
 10. A method for producing a device according to claim1 wherein one or more of the layers present in the device are formed bycarrying out procedural steps (i) and (ii) sequentially one or moretimes: (i) printing and (ii) drying the printed layer.
 11. A method forproducing a device according to claim 1, wherein a surface layer isprovided; and wherein the other layers of the device are appliedsequentially according to the sequence of their arrangement in thedevice; and wherein at least upon applying the indicator layer and theactivator layer the layer which is applied first is dried prior toapplying a subsequent layer, and the component or components of thesubsequent layer are provided and applied in a highly volatile organicsolvent if no additional layer is provided between the indicator layerand the activator layer.
 12. Packaging for a deep frozen productcomprising the device according to claim
 1. 13. A deep frozen productcomprising the packaging according to claim
 12. 14. The device accordingto claim 2, wherein the pH indicator is an anthocyanin colorant.
 15. Thedevice according to claim 4, wherein the at least one hygroscopic saltis chosen from the group consisting of magnesium chloride, potassiumchloride and calcium chloride.
 16. The device according to claim 1,further comprising: (d) a delaying layer (4), wherein the surface layeris positioned over the delaying layer, and the indicator layer ispositioned between the surface layer and the delaying layer.
 17. Thedevice according to claim 16, wherein the delaying layer (d) is formedfrom paper or cardboard with a thickness of 40-60 g/cm².
 18. The deviceaccording to claim 16, wherein the layers (a), (b), (c) and (d) arearranged as follows: (a) surface layer (1), (b) indicator layer (2), (d)delaying layer (4), and (c) activator layer (3); or (a) surface layer(1), (c) activator layer (3), (b) indicator layer (2), and (d) delayinglayer (4); or (a) surface layer (1), (b) indicator layer (2), (c)activator layer (3), and (d) delaying layer (4).
 19. A method forproducing a device according to claim 16 selected from the followingmethods: (a) A method comprising the following steps: (A-1) providingthe surface layer (1), (A-2) coating the surface layer (1) with theindicator layer (2), (A-3) drying the indicator layer (2) to produce anarrangement (A); (B-1) providing a delaying layer (4), (B-2) coating thedelaying layer (4) with the activator layer (3), (B-3) drying theactivator layer (3) to produce an arrangement (B), (C) laminating thearrangements (A) and (B); and (b) A method comprising the followingsteps: (A′-1) providing the surface layer (1), (A′-2) coating thesurface layer (a) with the activator layer (3), (A′-3) drying theactivator layer (3) to produce an arrangement (A′) (B′-1) providing adelaying layer (d) (B′-2) coating the delaying layer (d) with theindicator layer (2), (B′-3) drying the indicator layer (2) to produce anarrangement (B′), (C′) laminating the arrangements (A′) and (B′).
 20. Amethod for producing a device according to claim 16, wherein a firstlayer, chosen from the surface layer and the delaying layer, isprovided; and wherein the other layers of the device are appliedsequentially according to the sequence of their arrangement in thedevice; and wherein at least upon applying the indicator layer and theactivator layer the layer which is applied first is dried prior toapplying a subsequent layer, and the component or components of thesubsequent layer are provided and applied in a highly volatile organicsolvent if no additional layer is provided between the indicator layerand the activator layer.